Position compensating differential locking mechanism

ABSTRACT

A differential with an improved locking mechanism is provided. The differential includes first and second clutch members in the form of a differential case having a first set of teeth and a an axle shaft mounted clutch collar having a second set of teeth. A yoke urges the clutch into an out of engagement and is supported on a pivot shaft. The yoke is selectively urged in one direction by an actuator acting on a lever on the pivot shaft. The lever is coupled to the yoke by a spring. The yoke is urged in an opposite direction by one or more return springs mounted on the same pivot shaft. The compact nature of the locking mechanism and the balance of forces provided by the springs and actuator provide an inexpensive and reliable locking mechanism.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a differential, and moreparticularly, to a position compensating differential locking mechanism.

[0003] 2. Discussion of Related Art

[0004] Differential gear mechanisms, simply referred to asdifferentials, are well known devices frequently used in the drivetrains of most vehicles. The differential is usually connected betweenan input driving shaft {typically a drive shaft from the vehicle engine}and a pair of output driven shafts (typically a pair of axle shaftsconnected to the vehicle wheels). The differential distributes torquefrom the input shaft equally to the two output shafts, while permittingsuch output shafts to rotate at different speeds under certainconditions. As a result, torque is supplied to both wheels of thevehicle as it negotiates a turn, while permitting the outside wheel toturn faster than the inside wheel.

[0005] In a conventional open differential, the movements of the variousinternal components of the differential are not restricted in anysignificant fashion. Thus, the differential functions in the desirablemanner described above under most circumstances. However, when one ofthe wheels loses traction with the ground, due to, for example, wet oricy surfaces, the differential will reduce the amount of torque suppliedto the other wheel. Consequently, the vehicle can become immobilized.

[0006] To prevent immobilization, some differentials are provided with alocking mechanism. When actuated, the locking mechanism restricts themovement of some of the differential's internal components. Thisrestriction allows the drive shaft to provide torque to both wheelsinstead of providing torque only to the wheel with less traction. Somedifferential locks remain locked and automatically unlock while turningcorners. Other differentials use a driver-initiated control to manuallyengage and disengage the lock at the driver's command.

[0007] One conventional differential locking mechanism includes a firstset of teeth on a differential case of the differential and a clutchcollar having a second set of teeth configured to selectively engage thefirst set of teeth. The clutch collar is supported on a drive axle shaftextending through the differential case. The mechanism further includesa yoke supported on a pivot shaft and received within a groove in theclutch collar. A lever is also supported on the pivot shaft and isdisposed outside of the differential housing where it may be coupled toa spring-loaded cable system manually operated by the vehicle operator.This conventional differential has several disadvantages. First, thelocking mechanism can only be engaged while the vehicle is at rest.Second, the manual engagement of the locking mechanism requires aphysical effort on the part of the operator. Third, the lockingmechanism requires a relatively large amount of space to link the leverand the cable system.

[0008] The inventors herein have recognized a need for a differentialthat will minimize and/or eliminate one or more of the above-identifieddeficiencies.

SUMMARY OF THE INVENTION

[0009] The present invention provides a differential with a positioncompensating differential locking mechanism.

[0010] A differential in accordance with one embodiment of the presentinvention includes a differential case having a first set of teeth anddefining a central bore. A drive axle shaft is disposed within thecentral bore and is rotatable therein. The differential also includes aclutch collar mounted on the drive axle shaft. The clutch collar has asecond set of teeth configured to selectively engage the first set ofteeth and to prevent relative rotation between the drive axle shaft andthe differential case. The clutch collar further defines a groove. Ayoke is supported on a pivot shaft and is received within the groove inthe clutch collar. The differential further includes a lever supportedon the pivot shaft and a first spring disposed between the yoke and thelever. An actuator selectively urges the lever and the yoke in a firstrotational direction to a first position. A second spring urges thelever and the yoke in a second rotational direction to a secondposition. The first and second sets of teeth are urged into engagementin one of the first and the second positions and the first and thesecond sets of teeth are urged to disengage in another of the first andthe second positions.

[0011] A differential in accordance with the present invention has oneor more advantages as compared to the prior art. First, the differentialcan operate freely during vehicle travel regardless of the level ofengagement between the opposed clutch members. Second, the inventivedifferential may eliminate the need for manual operation of thedifferential locking mechanism. Third, the locking mechanism of theinventive differential is compact thereby conserving vehicle space.

[0012] This and other features and objects of this invention will becomeapparent to one skilled in the art from the following detaileddescription and the accompanying drawings illustrating features of thisinvention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a cross-sectional view of a differential in accordancewith one embodiment of the present invention.

[0014]FIG. 2 is an exploded view of a portion of the differential ofFIG. 1.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0015] Referring now to the drawings wherein like reference numerals areused to identify identical components in the various views, FIG. 1illustrates a cross-sectional view of a differential 10 in accordancewith one embodiment of the present invention. Differential 10 isprovided to enable two wheels (not shown) in a vehicle that are disposedabout a common rotational axis to rotate at different speeds.Differential 10 may include several conventional components known tothose of skill in the art. In particular, differential 10 may include ahousing 12 composed of multiple members and a pinion shaft 14 thatextends through an opening in housing 12 and supports a pinion gear 16.The pinion shaft 14 may be supported for rotation within housing 12 bybearings 18, 20 and may be driven by a power input shaft (not shown).Differential 10 may further include a ring gear 22 coupled to orintegral with a differential case 24 and driven by pinion gear 16. Case24 is supported within housing 12 by bearings 26, 28 and may house aspider 30 on which one or more differential gears 32, 34 are mounted.Gears 32, 34 mesh with side gears 36, 38 splined to drive axle shafts40, 42 that are disposed in central bores 44, 46, respectively, definedin case 24. Shafts 40, 42 are rotatable within bores 44, 46 about anaxis 48. In accordance with the present invention, differential 10 mayalso include a differential locking mechanism 50.

[0016] Referring to FIGS. 1 and 2, mechanism 50 is provided toselectively lock and unlock differential 10 to prevent relative rotationbetween shafts 40, 42. Mechanism 50 may include a clutch collar 52, ayoke 54, a pivot shaft 56, a lever 58, an actuator spring 60, anactuator 62, and one or more return springs 64, 66.

[0017] Clutch collar 52 comprises one member of a clutch used to lockdifferential 10 and thereby prevent relative rotation between shaft 40and case 24. Collar 52 defines a bore 68 configured to received shaft40. Collar 52 is mounted on shaft 40 and is axially movable on shaft 40through, for example, splines disposed on a radially outer surface ofshaft 24 and a radially inner surface of collar 52. Collar 52 mayinclude a set of teeth 70 at one axial end of collar 52 configured toselectively engage another set of teeth 72 on one axial end of case 24.Teeth 70 on collar 52 may be machined with a negative one-degree draftto aid in retaining engagement between teeth 70, 72 during rotation.Collar 52 also defines a peripheral, circumferentially extending groove74 proximate another axial end of collar 52.

[0018] Yoke 54 is provided to move collar 52 axially inboard andoutboard and to thereby move teeth 70 on collar 52 into and out ofengagement with teeth 72 on case 24. Referring to FIG. 2, yoke 54includes a substantially U-shaped member 76 configured to be receivedwithin groove 74 of collar 52. Yoke 54 may further include asubstantially U-shaped bracket 78 coupled to member 76 through welds orother conventional fasteners. Bracket 78 opens in an opposite directionas compared to member 76 and includes aligned apertures 80, 82 proximateeach end enabling yoke 54 to be supported on pivot shaft 56.

[0019] Pivot shaft 56 enables pivoting motion of yoke 54 and lever 58.Shaft 56 is supported at either longitudinal end within one or morebores 84, 86 in housing 12 as shown in FIG. 2. Bushings (not shown) maybe interposed between the inner surface of housing 12 defining bores 84,86 and shaft 56. Shaft 56 extends through apertures 80, 82 in bracket 78of yoke 54.

[0020] Lever 58 is provided for use in causing rotation of yoke 54 aboutpivot shaft 56. Lever 58 includes an aperture 86 through which shaft 56extends to support lever 58. Lever 58 is free to rotate about shaft 56and is disposed between the opposed ends of bracket 78. Lever 58 furtherdefines a groove 88 configured to receive a portion of spring 60.

[0021] Spring 60 couples yoke 54 and lever 58 and is disposed betweenyoke 54 and lever 58. Spring 60 may comprise a double coil springwherein the coils are sized to receive pivot shaft 56. Spring 60includes two tangs 90, 92 that are coupled to yoke 54 and spring 60 isreceived within the opposed ends of bracket 78.

[0022] Actuator 62 is provided to selectively urge lever 58 and yoke 54in one rotational direction (clockwise in the illustrated embodiment) toone of two positions. In the illustrated embodiment, yoke 54 is moved toa position that results in disengagement of teeth 70, 72 from oneanother. It should be understood, however, that actuator 62 couldalternatively urge yoke 54 in the opposite rotational direction toanother position that results in engagement of teeth 70, 72. In apreferred embodiment of the invention, actuator 62 comprises anelectronic actuator and, in particular, a push-type solenoid. It shouldbe understood, however, that actuator 62 may take on a variety of formsincluding, for example, a magnetic latch type solenoid. Actuator 62includes a plunger 94 that is selectively urged outwardly from actuator62 to engage lever 58 and cause rotation of yoke 54.

[0023] Return springs 64, 66 are provided to urge yoke 54 in anotherrotational direction (counterclockwise in the illustrated embodiment),opposite to the rotational direction urged by actuator 62, and toanother position. In the illustrated embodiment, this position resultsin engagement of teeth 70, 72. It again should be understood, however,that return springs 64, 66 could alternatively urge yoke 54 in theopposite direction to a position resulting in disengagement of teeth 70,72. Return springs 64, 66 include a coil sized to receive pivot shaft 56and are located on pivot shaft 56 on either side of bracket 78 of yoke54. Springs 64, 66 are coupled to yoke 54 at one end and at housing 12at another end. Although two return springs 64, 66 are shown in theillustrated embodiment, it should be understood that varying numbers ofsprings could be used without departing from the spirit of the presentinvention.

[0024] Referring again to FIGS. 1 and 2, in the illustrated embodimentreturn springs 64, 66 normally urge yoke 54 in a first rotationaldirection causing axial movement of collar 52 in an inboard directiontowards case 24 and engagement of teeth 70, 72. In one constructedembodiment, springs 64, 66 exert about 1.5 lbs. of force. Disengagementof teeth 70, 72 is accomplished by energizing actuator 62 using acontrol signal (not shown) generated by the vehicle operator or aprogrammable microcontroller (not shown). In one constructed embodiment,the plunger 94 of actuator 62 initially is driven by 12 V_(DC). Thiscurrent causes plunger 94 to move approximately 0.220 inches and plunger94 exerts an initial force of about 10 lbs. at the start and 13.5 lbs.once fully extended. After extension, 3 V_(DC) is used to maintainplunger 94 in place and a holding force of about 9 lbs is exerted byplunger 94. Extension of plunger 94 causes rotation of lever 58 aboutshaft 56. Because teeth 70, 72 remained engaged under the torque of axleshaft 40, rotation of lever 58 compresses spring 60 creating a torsionalload or spring force of about 7.5 lbs acting against yoke 54 in oneconstructed embodiment. Upon a reduction in torque in axle shaft 40,spring 60 forces yoke 54 to rotate in a clockwise direction to aposition in which teeth 70, 72 become disengaged. One advantage of thepresent invention is that the compression of spring 60 by the initialrotation of lever 58 in response to plunger 94 creates a secondary forceurging yoke 54 away from lever 58 thereby reducing the force requiredfrom actuator 62. As yoke 54 pivots, the tension in spring 60 decreaseswhile the tension in return springs 64, 66 increases until the opposingforces are balanced. The use of springs 60 and 64, 66 in the presentinvention is advantageous because springs 60 and 64, 66 allowindependent adjustment of the forces urging yoke 54 in either rotationaldirection and, consequently, clutch collar 52 in either axial direction.For example, selecting the balance of these spring forces determines theextent to which clutch collar 52 will move axially outboard from case 24upon disengagement.

[0025] Upon deenergization of actuator 62, or a failure in the powersource for actuator 62, return springs 64, 66 urge yoke to a position inwhich teeth 70 of clutch collar 52 and teeth 72 of case 24 becomeengaged. Movement of yoke 54 also causes corresponding movement of lever58 through spring 60 thereby urging plunger 94 into a retracted positionin actuator 62. In the embodiment shown in FIG. 1, springs 64, 66 urgeyoke 54 to rotate in a counterclockwise direction thereby causing collar52 to move axially in an inboard direction.

[0026] A differential in accordance with the present inventionrepresents an improvement over prior art differentials. The inventivedifferential can operate freely during vehicle travel regardless of thelevel of engagement between the teeth 70, 72 on the clutch collar 52 anddifferential case 24. The inventive differential may also eliminate theneed for manual operation of the differential locking mechanism throughuse of an electronically controlled actuator 62. The locking mechanismof the inventive differential is also compact with lever 58 disposedinside the differential housing 12 thereby conserving vehicle space.

[0027] While the invention has been particularly shown and describedwith reference to the preferred embodiment thereof, it is well known bythose skilled in the art that various changes and modifications can bemade in the invention without departing from the spirit and scope of theinvention as defined by the following claims.

We claim:
 1. A differential comprising: a differential case having afirst set of teeth and defining a central bore; a drive axle shaftdisposed within said central bore and rotatable therein; a clutch collarmounted on said drive axle shaft, said clutch collar having a second setof teeth configured to selectively engage said first set of teeth and toprevent relative rotation between said drive axle shaft and saiddifferential case, said clutch collar further defining a groove; a yokesupported on a pivot shaft and received within said groove in saidclutch collar; a lever supported on said pivot shaft; a first springdisposed between said yoke and said lever; an actuator that selectivelyurges said lever and said yoke in a first rotational direction to afirst position; and a second spring that urges said lever and said yokein a second rotational direction to a second position; wherein saidfirst and said second sets of teeth are urged into engagement in one ofsaid first and said second positions and said first and said second setsof teeth are urged to disengage in another of said first and said secondpositions.
 2. The differential of claim 1 wherein urging said lever insaid first rotational direction compresses said first spring, said firstspring exerting a spring force urging said yoke in said first rotationaldirection.
 3. The differential of claim 2 wherein said first springremains compressed and said first and said second set of teeth remainengaged until said drive axle shaft experiences a reduction in torque.4. The differential of claim 1 wherein said actuator exerts an initialforce on said lever, said initial force followed by a holding force,said holding force being less than said initial force.
 5. Thedifferential of claim 1 wherein said actuator comprises an electronicactuator.
 6. The differential of claim 1 wherein said actuator comprisesa solenoid.
 7. The differential of claim 1 wherein said second set ofteeth have a negative one-degree draft.
 8. The differential of claim 1wherein said first spring is a double coil spring.
 9. A differentialcomprising: a differential case having a first set of teeth and defininga central bore; a drive axle shaft disposed within said central bore androtatable therein; a clutch collar mounted on said drive axle shaft,said clutch collar having a second set of teeth configured toselectively engage said first set of teeth and to prevent relativerotation between said drive axle shaft and said differential case, saidclutch collar further defining a groove; a yoke supported on a pivotshaft and received within said groove in said clutch collar; a leversupported on said pivot shaft; a first spring disposed between said yokeand said lever; an actuator that selectively urges said lever and saidyoke in a first rotational direction to a first position, said firstposition being achieved when said first set of teeth are disengaged fromsaid second set of teeth; and a second spring that urges said lever andsaid yoke in a 20 second rotational direction to a second position, saidsecond position being achieved when said first set of teeth aredisengaged from said second set of teeth.
 10. The differential of claim9 wherein said first spring remains compressed and said first and saidsecond set of teeth remain engaged until said drive axle shaftexperiences a reduction in torque.
 11. The differential of claim 9wherein said actuator exerts an initial force on said lever, saidinitial force followed by a holding force, said holding force being lessthan said initial force.
 12. The differential of claim 9 wherein saidactuator comprises an electronic actuator.
 13. The differential of claim9 wherein said actuator comprises a solenoid.
 14. The differential ofclaim 9 wherein said second set of teeth have a negative one-degreedraft.
 15. The differential of claim 9 wherein said first spring is adouble coil spring.
 16. A differential comprising: a differential casehaving a first set of teeth and defining a central bore; a drive axleshaft disposed within said central bore and rotatable therein; a clutchcollar mounted on said drive axle shaft, said clutch collar having asecond set of teeth configured to selectively engage said first set ofteeth and to prevent relative rotation between said drive axle shaft andsaid differential case, said clutch collar further defining a groove; ayoke supported on a pivot shaft and received within said groove in saidclutch collar; a lever supported on said pivot shaft; a double coilspring disposed between said yoke and said lever; a solenoid thatselectively urges said lever and said yoke in a first rotationaldirection to a first position upon energization, said first positionbeing achieved when said first set of teeth are disengaged from saidsecond set of teeth; and at least one return spring that urges saidlever and said yoke in a second rotational direction to a secondposition, said second position being achieved when said first set ofteeth are disengaged from said second set of teeth.
 17. The differentialof claim 16 wherein said double coil spring remains compressed and saidfirst and said second set of teeth remain engaged until said drive axleshaft experiences a reduction in torque.
 18. The differential of claim16 wherein said solenoid exerts an initial force on said lever, saidinitial force followed by a holding force, said holding force being lessthan said initial force.
 19. The differential of claim 16 wherein saidsecond set of teeth have a negative one-degree draft.